The present invention generally relates to the blood dialysis and, more particularly, to a method for blood dialysis and an apparatus for the removal of waste products of metabolism from the blood by the use of a dialyzer. The method and apparatus herein disclosed according to the present invention are effectively utilized for the automation of the blood dialysis at a minimized energy-consumption.
A technique of blood dialysis by the use of a dialyzer, or an artificial kidney as it is generally known, has long been widely practiced to purify the human blood by the removal of waste products of metabolism in the body of a patient with the dialyzer functioning in lieu of a kidney in the case of the kidney failure.
Since the method and apparatus to which the present invention pertains is concerned with the utilization of a positive ultrafiltration pressure in the dialyzer for the diffusion of waste products of metabolism from the blood into the dialyzing solution, the prior art system wherein the positive ultrafiltration pressure is similarly utilized will now be discussed in detail with particular reference to FIG. 1 of the accompanying drawings.
FIG. 1 illustrates schematically an extra-corporeal blood circuit extending from an artery to a vein, for example, from a radial artery to a saphenous vein of a patient A, in which circuit the prior art dialyzing apparatus is placed. The extracorporeal blood circuit shown therein includes an inlet cannula 1a, inserted into the radial artery, and an outlet cannula 1b inserted into the saphenous vein. According to the prior art, the blood to be dialyzed and flowing into the inlet cannula 1a is pumped by a blood pump 2 so as to flow towards a dialyzer unit 3 through a tubing 5a and then towards the outlet cannula 1b through a tubing 5 after having passed through a blood chamber in the dialyzer unit 3. The blood so flowing to the outlet cannula 1b after the waste products of metabolism have been removed therefrom is eventually returned to the saphenous vein of the patient A. In addition to the blood chamber, the dialyzer unit 3 has a dialysate chamber communicating through a solution inlet 8a to a source of dialyzing solution on the hand and through a dialysate outlet 8b to any suitable dialysate disposing container on the other hand. In order to achieve the positive ultra-filtration, that is, in order to create a pressure difference between the flow of the blood within the blood chamber and that of the dialyzing solution within the dialysate chamber to enable the waste products of metabolism contained in the blood to be forced into the dialysing solution through a membrane within the dialyzer unit 3, the tubing 5 on the downstream side with respect to the direction of flow of the blood towards the outlet cannula 1b has a flow regulator 4 for adjustably constricting the tubing 5. For monitoring the ultrafiltration pressure, a portion of the tubing 5a between the pump 2 and the dialyzer unit 3 and a portion of the tubing 5 between the dialyzer unit 3 and the flow regulator 4 have respective air traps 6a and 6b disposed thereon and fluid-coupled to associated pressure gauges 7a and 7b.
When in use for the blood dialysis, the blood pump 2 is operated to effect the extracorporeal circulation of the blood through the extracorporeal blood circuit by way of the dialyzer unit 5 while the flow regulator 4 is adjusted in the light of readings of the pressure gauges 7a and 7b to create a proper positive ultrafiltration pressure.
As is well known to those skilled in the art, a primary function of the kidney is to form urine, the main constituent of which is a water component. Accordingly, when it comes to the blood dialysis, the removal from the blood of an excessive water component containing the waste products of metabolism is one of the major concerns that cannot be neglected. In other words, while the water component within the body is transferred into the blood having flowed within the cells and then into the blood vessels through the interstices among the cells, the removal of the excessive water component containing the waste products of metabolism has to be done at a rate conforming to the rate of transfer of the water component into the blood. However, not only because the rate of transfer of the water component into the blood differ from patient to patient, but also because for a patient it changes with time each day, it is not easy to grasp it without difficulty. In addition, the water removal is affected by numerous factors such as, for example, the ultrafiltration pressure, the type and the total surface area of the semipermeable membrane or membranes used in the dialyzer unit, the time during which the dialysis is carried out, the rate of flow of the blood and the difference in osmotic pressure between the dialyzing solution and the blood.
Of these factors, the type and the total surface area of the semipermeable membrane or membranes are determined by the type of dialyzer unit employed, and accordingly, by suitably selecting a particular type of dialyzer unit to be employed, the problem associated therewith can be solved. The difference is osmotic pressure between the dialyzing solution and the blood has been found not affect the water removal appreciatively. With respect to the dialyzing interval, that is, the time during which the dialysis is carried out, the longer, the greater the amount of water removed. However, the shorter, the better, because if it extends for a long time, not only is the patient required to be bound to the dialyzing facility, but also care must be taken to water the patient for such a long time.
In view of the foregoing, it can be deduced that in practice the blood dialysis has to be carried out at a controlled blood flow and under a controlled ultrafiltration pressure and both are required to facilitate the removal of the water component so that the required amount of the water component can be removed in a given time interval. For this purpose, the major factor is the stabilized flow of blood through the extracorporeal blood circuit from the patient back to the same patient. However, the blood flow through the extracorporeal blood circuit is limited depending on the physical conditions of a particular patient. In addition, it is extremely difficult for the stabilized flow of blood through the extracorporeal blood circuit to be maintained for a substantially prolonged time partly because a drop in blood pressure would occur as a result of insufficient blood circulation within the patient's body which will occur as a result of the accelerated water removal and partly because of any possible malfunctioning of A-V fistula equipment necessary to draw the blood exteriorly of the patient's body. In particular, the patient suffering from hypotonia as a result of the accelerated water removal during the blood dialysis tends not only to feel discomfort causing, for example, a symptom of vomiting, but also to have a bodily convulsion which, unless care is taken of the patient, will last for a substantial time interval and will, in the worst case, result in death from shock. Accordingly, the utmost care is required once the symptom of hypotonia has been observed in the patient being dialyzed.
On the other hand, if the rate of water removal is lowered for fear of the hypotonia, that is, the drop in blood pressure, during the blood dialysis, no sufficient and satisfactory water removal will be performed with some of the waste products of metabolism consequently left unremoved, imposing an undesirable burden on the blood circulatory system.
Hitherto, regulator blood pressure measurement, that it, a regular sphygnomanometric measurement, is frequently carried out as a precaution against any possible drop in blood pressure which would result from the accelerated water removal. By way of example, in the case of a chronic patient whose kidney failure is substantially stabilized and is, therefore, familiar to the attendant doctor, the blood pressure measurement is carried out at intervals of 15 and 30 minutes at the time of start of the dializing treatment, of 30 to 60 minutes during the course of the treatment, or of 15 to 30 minutes before the termination of the treatment. On the other hand, in the case of the patient receiving the dialyzing treatment for the first time, in the case of the patient being a child or an aged person whose amount of blood being circulated is relatively small, or in the case of the patient who is suffering from, for example, a diabetic disease accompanied by severe arteriosclerosis and who is, therefore, susceptible to hypotonia or coronary insufficiency, the blood pressure measurement is carried out at a number of times greater than that required for routine blood pressure measurement while the rate of the water component being removed is adjusted according to the result of each measurement.
In any event, a qualified nurse is usually charged, under instructions of a doctor, with the work of blood pressure measurement and, if necessary, the adjustment of the rate of water removal. However, once the patient suffers from hypotonia during the dialyzing treatment, the nurse is caused to be busy not only with the regular nursing procedures, but also with extra nursing procedures including, for example, the performance of a transfusion, the administration of drugs, and application of hot or cold dressing, and sanitary matters. Considering that one qualified nurse is assigned to take care of four or five patients, these works occupy a high percentage of the nursing job and, therefore, the nurse is often forced to work hard.
Thus, according to the prior art, the requirement of manual intervention is too high in performing a plurality of such works required to achieve the blood dialysis under satisfactory and effective conditons with the use of a conventional dialyzing method and apparatus, and therefore, numerous problems have arisen such as the increased possibility of occurrence of errors on the part of the caretaker, the heavy labour imposed on the nurse, and the cost incurred not only by a patient, but also by a hospital.